As is known, internal combustion engines of the type disclosed in Italian Patent Application BO99A000443 filed on 4 Aug. 1999, are currently being tested, in which the intake and exhaust valves are moved by electromagnetic actuators. These electromagnetic actuators have undoubted advantages, as they make it possible to control each valve according to a law optimised for any operating condition of the engine, while conventional mechanical actuators (typically camshafts) make it necessary to define a lift profile for the valves which represents an acceptable compromise for all the possible operating conditions of the engine.
An electromagnetic actuator for a valve of an internal combustion engine of the type described above normally comprises an actuator body, which is connected to the stem of the valve and, in rest conditions, is held by at least one spring in an intermediate position between two de-excited electromagnets; in operation, the electromagnets are controlled so as alternately to exert a force of attraction of magnetic origin on the actuator body in order to displace this actuator body between the two limit abutment positions, which correspond to a position of maximum opening and a position of closure of the respective valve.
In order to displace the valve from the position of maximum opening to the closed position or vice versa, the actuator body has to be displaced from a position of abutment against a first electromagnet to a position of abutment against a second electromagnet; for the purposes of performing this displacement, the first electromagnet is de-excited and the second electromagnet is subsequently excited with the excitation parameters, i.e. with values of intensity, duration and instant of commencement of the excitation current, depending on the engine point.
It has been observed, however, that in the known electromagnetic actuators of the type described above, the position of abutment against the second electromagnet is normally reached with a relatively high speed of impact of the actuator body against the second electromagnet, which causes both substantial mechanical stresses on the electromagnetic actuator and a high level of noise generated by the electromagnetic actuator.
In order to attempt to remedy the above-described drawbacks, it has been proposed to use an external position sensor, which provides, instant by instant, the exact position of the actuator body and makes it possible precisely to control the actual position of the actuator body; position sensors able to provide the precision and service life needed for profitable use for this purpose are not, however, commercially available.